poster girl KILLED FIGHTING ISIS

CHEMICAL ATTACK

The first week of the truce will be crucial. During that time, all fighting between the military of President Bashar Assad and rebels is to stop.

However, the al-Qaeda linked insurgents are closely allied to many rebel factions and are a powerful force in the defence of Aleppo in particular.

That raises the danger that continued airstrikes will draw rebels into retaliation, eventually leading to the cease-fire's collapse, much as previous attempts earlier this year fell apart.

Compounding the situation, a group of 21 rebel factions issued a statement Friday in which they warned against targeting al-Qaida-linked militants.

AP:Associated Press

President Bashar al-Assad walks through street in Daraya, a suburb recently liberated by government forces

The statement was non-committal about whether the groups would abide by the cease-fire.

After a week, however, the conflict would potentially enter a dramatically different stage. A new U.S.-Russia coalition will step in to target former Nusra Front militants, and Assad's forces will no longer be permitted to.

That will effectively remove Assad's pretext for war on opposition areas, which he calls a war on terror.

Government forces will be allowed to fight defensively, target ISIS and, in some designated areas, go after Nusra forces.

The deal's architects hope that would pave the way for an extended period of restraint that can serve as the foundation for peace talks between the war's many sides.

AP:Associated Press

Russian military leaders (pictured) said they would continue strikes against ISIS

As the cease-fire came into effect, U.S. Secretary of State John Kerry said Monday that rebel factions must distance themselves from the al-Qaida-linked militants, whose group recently changed its name from Nusra to Jabhat Fatah al-Sham, or Levant Conquest Front.

He also said the Syrian government must allow deliveries of humanitarian aid into besieged areas, including the rebel-held districts of Aleppo.

Russia's Deputy Foreign Minister Mikhail Bogdanov said peace talks between opposition groups and the government could resume as early as next month.

The war has raged for five-and-a-half years, continuing the grinding violence that has so far killed more than 250,000 people and driven some 11 million people, half of Syria's population, from their homes since 2011.

We pay for your stories! Do you have a story for The Sun Online news team? Email us at tips@the-sun.co.uk or call 0207 782 4368.